The present invention relates generally to tuning systems and more particularly to all channel electronic television tuning systems having a time-sequenced counting system for deriving the channel number of a receivable television signal from the frequency of the local oscillator and a comparator-controlled source of tuning voltage. The receiver is tuned by comparing the derived channel number with a desired two digit channel number. Specifically, it relates to an interactive display system for visually indicating the channel number of the receivable television signal.
U.S. Pat. No. 3,671,896 to Wolfram shows a channel indicator employing a two digit segmented display device for channel numbers. A limited number of double-throw switches, each having simultaneously operable tens and units poles, are wired to encoding matrices to cause the display devices to display the channel number of the correspondingly wired switch.
A paper by Sakamoto and Ichinohe (BTR, Vol. 18, No. 3, Aug., 1972) includes a very limited description of a channel selection and display system employing a plurality of individual preset potentiometers, for applying voltages to a varactor tuner, which are identifiable by channel numbers. Access is through a ten digit keyboard coupled to an 8 bit shift register for enabling logic gates in a matrix. No operational details are given.
Since the FCC allocated channel numbers extend from 2 through 83, both one digit and two digit channel numbers are employed. All-channel tuners must therefore accommodate selection of both dual digit and single digit channel numbers. A digit entry tuning system may provide a separately activated tuning command switch, operable after channel number selection, or respond only to entry of both digits of two digit channel numbers. This latter system should distinguish between the entry of a 2 for tuning channel 2 and a 2 as the first digit of channel 20. An inadverdent or mistaken entry of a single digit will cause mistuning and frustration on the part of the viewer unless some indication of an improper entry is provided. The prior art, as indicated above, discloses a number of digital tuning systems having displays of a tuned channel number but none employ a display device in an interactive manner to indicate when a complete channel number has been selected.